1. Field of the Invention
The present invention relates generally to balloon catheters of the type that are inserted into the vascular system. More particularly, the invention relates to a system and method for detecting the presence of minute quantities of a contaminant, such as blood, within the balloon chamber of a balloon catheter. The invention is believed to offer three particularly useful advantages: (1) it permits sensitive and early detection of failure of membrane integrity should the membrane be damaged, as during an intra-aortic procedure using a balloon catheter, (2) it provides a method for determining significant deterioration of the system, and (3) it permits detection of leakage of a contaminant such as blood into the balloon chamber much more rapidly than was previously possible by traditional methods.
2. Related Background
Balloon catheters having use in medical procedures requiring introduction into the vascular system are well known. Such catheters typically have a catheter portion with proximal and distal ends, and a balloon portion located at or near the distal end of the catheter portion.
The balloon catheter for which the subject invention is believed to be most useful is the intra-aortic balloon catheter. The invention herein disclosed, however, is not limited to use in such devices.
Conventional intra-aortic balloon catheters have non-distensible balloons that conventionally are inflated with either helium or carbon dioxide provided through the catheter portion by an external pump console connected at the proximal end of the catheter. The catheter portions are preferably quite flexible as well as soft, in order to facilitate their negotiation through the vascular system. The entire balloon catheter may have a length of up to two and a half to three feet, with the balloon portion comprising up to ten inches. Typically, the balloon chamber, when inflated, has a volume of about 40 cc, although larger and smaller balloons are not uncommon.
It is well known that atherosclerotic plaques, for example, can be quite hard and may have sharp edges. Consequently, the possibility exists that balloons or other portions of balloon catheters may be damaged or punctured by the plaques or other deposits within the vascular system. Such damage could cause leakage of the inflating gas into the patient's vascular system, as well as leakage of blood into the balloon chamber. Therefore, prompt detection of any damage to the balloon is of the utmost importance.
Detection of such damage has previously been very difficult. For example, intra-aortic balloon catheters typically contain gas in a closed system. A fixed volume of gas is pumped or shuttled back and forth between the balloon resident in the patient's aorta and the balloon in the pump console. If the integrity of the balloon within the body of the patient is compromised, gas will leak from the closed system into the blood vessel of the patient and the reduction in gas volume will trigger an alarm, alerting the operator. However, the volumetric triggers of such closed system catheters have certain limitations. Typically, they cannot be made adequately sensitive without risking frequent false alarms. Consequently, these volumetric triggers generally do not respond until a significant amount of gas has escaped from the closed system.
The instant invention overcomes the drawbacks of volumetric sensors by using a light reflector/detector system. Light is transmitted through an optical fiber to the balloon chamber where it is reflected back to a sensor. Any change in reflected light, whether it be in intensity, color or the like, can then be detected and used to trigger the alarm.
It has been found that when the balloon membrane has been damaged, not only does inflating gas tend to escape, but, in addition, blood also tends to enter the balloon chamber. The instant invention, instead of reacting to a reduced gas volume, reacts to the presence of blood, or some other contaminant, in the chamber. Since the presence of even the smallest amount of blood inside the balloon is cause for concern, the detection system of the instant invention can be made far more sensitive, and with greater rapidity of response, than volumetric detectors.
In other arts, fiber optical probes have been used to determine, for example, pH and properties of chemical in living tissue. To illustrate, Costello U.S. Pat. No. 4,682,895 relates to a fiber optic probe that includes two optical fibers enclosed in a semipermeable membrane. A colorimetric substance is contained in a sample chamber. A sample chemical permeates the membrane and the colorimetric substance. If the property to be tested is present in the chemical, the colorimetric substance will change color and its transmissivity will be altered, signalling the presence of the property to be detected. According to Costello, light transmitted along the optical fiber traverses the sample chamber and is detected by another optical fiber that is disposed opposite to the transmitting fiber. Such a system, however, only considers the specific chemical property to be tested, and cannot detect the presence of contaminants.
Peterson, et al. U.S. Pat. No. 4,200,110 relates to a fiber optic probe for determining the pH of living tissue. A pH sensitive dye is provided within an ion permeable membrane that encloses the ends of two optical fibers. Peterson's probe determines pH based on a change in color of the pH sensitive dye. This probe, however, cannot detect the presence of contaminants.
Wicnienski U.S. Pat. No. 4,350,441 relates to a photometric system for determining an absorbance ratio of two different wavelengths of light passed alternately through a sample. A similar system is described in Bilstad, et al. U.S. Pat. No. 4,305,659.
According to Bilstad, et al., a first light is given a reference intensity, and a second light is varied so that its intensity matches that of the first light after it passes through a sample. Absorbance is calculated based on a ratio of the absorbance of the second light where its intensity is equal to a state in which it has not passed through a sample, and the absorbance of the first light. Neither system is designed to determine the presence of contaminants in a catheter, nor do they solve the above-described problems of traditional methods for detecting catheter failure.